The present project has three main objectives: (a) To perfect the instrumentation necessary to analyze the fluorescence of proteins or protein conjugates or adsorbates with fluorophores; (b) To study ligand-protein interactions by fluorescence; (c) To investigate more complex model systems involving proteins and other components by fluorescence techniques in order to understand the behavior of proteins in natural systems. Under heading (a) we will continue the development of differential phase fluorometry to measure molecular rotations and solvent relaxation phenomena, including relaxations of the protein structure about fluorophores. In (b) our main effort is in the direction of detecting anisotropic rotation in the various protein-fluorophore complexes and also in the preparation of new fluorescent probes sensitive to the enviroment. Under (c) we shall study the effect of fluorescent ligands on the partition between protein and second phase. Some preliminary results of interest have been obtained already using serum albumin in water at pH 2.0. We shall also continue our studies of the effect of high pressures (1-10 kbars) upon the fluorescence of proteins. BIBLIOGRAPHIC REFERENCES: Quantitative Demonstration of the Reciprocity of Ligand Effects in the Ternary Complex of Chicked Heart Lactate Dehydrogenase with Nicotinamide Adenine Dinucleotide and Oxalate, D. A. Kolb and G. Weber, Biochemistry 14, 4471-4476 (1975). Cooperativity of Binding of Anilino-Naphthalene Sulfonate Induced by a Second Ligand, D. A. Kolb and G. Weber, Biochemistry 14, 4476-4481 (1975).